Tetrarhodium dodecacarbonyl


Tetrarhodium dodecacarbonyl is the chemical compound with the formula Rh412. This dark-red crystalline solid is the smallest stable binary rhodium carbonyl. It is used as a catalyst in organic synthesis.

Structure, synthesis, reactions

The structure of Rh412 is described by a tetrahedral array of four Rh atoms with nine terminal CO ligands and three bridging CO ligands. The structure can be expressed as Rh493. It is prepared by treatment of an aqueous solution of rhodium trichloride with activated copper metal under an atmosphere of CO.
Alternatively, the compound can be prepared by treatment of a methanolic solution of RhCl33 with CO to afford H, followed by carbonylation in the presence of sodium citrate.
The cluster undergoes thermal substitution with phosphorus ligands, L:

Related metal carbonyls

Because of their relevance to hydroformylation catalysis, the metal carbonyls has been systematically studied to a high degree. The instability of Rh28 has been a source of curiosity. The analogous binary carbonyl of cobalt, Co28, is well known. Solutions of Rh412 under high pressures of CO convert to the dirhodium compound:
Unlike Co28 which features bridging carbonyls, the main isomer of Rh28 features only terminal CO ligands. The relative instability of Rh28 is analogous to the tendency of Ru5 to convert to Ru312.

General reading